Paint Calculator
Find out how much paint to buy for a room. Enter the room size, the number of doors and windows, and how many coats you plan to apply.
Paint needed
1.8 gal
Check the highlighted fields to see your result.
- Area per coat
- 317 sq ft
- Total with all coats
- 634 sq ft
- To buy (+10%)
- 2.0 gal
We recommend buying 10% extra for waste and touch-ups.
Results are estimates for information only and do not constitute financial, medical, or legal advice.
How the paint is calculated
The calculator adds up the area of the four walls, subtracts a standard area for each door (20 sq ft or 2 m²) and window (15 sq ft or 1.5 m²), and adds the ceiling if you choose it. Then it multiplies by the number of coats and divides by the coverage of the paint.
The formulas
Walls = 2 × (length + width) × height − doors − windows
Paint = walls × coats ÷ coverage
Worked example
A room is 12 × 10 ft with 8 ft walls, one door, and one window. You'll apply 2 coats with paint that covers 350 sq ft per gallon.
- Walls: 2 × (12 + 10) × 8 = 352 sq ft.
- Minus the door and window: 352 − 20 − 15 = 317 sq ft.
- Two coats: 317 × 2 = 634 sq ft. Paint: 634 ÷ 350 = 1.8 gallons, so buy 2 gallons.
Frequently asked questions
Should I buy extra paint?
Yes. Buying around 10% more covers touch-ups, rough surfaces, and what's left in the roller and tray. Round up to the next can size.
Does primer count as a coat?
Not here. Primer is a different product with its own coverage, so work it out separately: enter 1 coat and the coverage printed on the primer can.
Why does the can say a different coverage?
Coverage depends on the paint and the surface. Rough, porous, or very dark walls take more paint. Use the number on your can for the best estimate.